Filters used in air purification systems must be periodically replaced after a certain period of operation, i.e., at the end of their service life, when they have deteriorated to the point of ineffectiveness. Adsorption cartridges should be replaced in due time, because a deteriorated filter cartridge is not effective in filtering out harmful substances from air. Replacement of adsorption cartridges usually takes place after contaminant break through, pressure drop, or after a certain operating period specified by the manufacturer. In order to be on the safe side, the life of such an adsorption cartridge specified by the manufacturer is determined on the basis of the most unfavorable operating conditions.
A disadvantage of this procedure is that in many instances the adsorption cartridges are replaced long before the end of their useful life, because the cartridges have been used under conditions much more favorable than those assumed by the manufacturer in determining the maximum permissible service life. In addition, administering a cartridge change schedule can be time-consuming, unnecessarily expensive, and cumbersome. Furthermore, contaminants, their concentration levels, temperature, and humidity all affect useful service life, and these variable factors are not adequately addressed by a time-based cartridge replacement schedule.
Real-time end of service life indicators provide an easier and more accurate way than cartridge replacement schedules to determine the service life of gas and vapor cartridges. Colorimetric indicators are available for some filtration cartridges. For example, a colorimetric indicator sensitive to mercury vapor gradually changes color when exposed to it. When the changing color matches the color guide on the cartridge exterior, it is time to change the cartridge.
A need exists, however, for a general method of indicating the useful service life of a gas filtration and purification system, especially a method and related equipment that provide an electronic indication of service life without the need to account for signal drift or interferents.